Stress tests on the home straight

27 April 2012

Nuclear operators in Europe have taken "significant steps to improve the safety of their plants" as a result of stress tests, said regulators from the continent in a review of each others' work on the program.

Inspired by the Fukushima accident, the European Commission's stress tests have examined the fundamental protection of some 147 nuclear reactors in 17 countries, including the non-EU states of Switzerland and Ukraine. The tests focused on external threats such as earthquake, tsunami and extreme weather as well as the loss of safety systems and severe accident management under any circumstances. Their goal was to uncover weaknesses in protection or procedures and identify any 'cliff-edge' factors beyond which a serious accident would become unavoidable.

Today came a report from the European Nuclear Safety Regulators Group (ENSREG), which detailed how the national regulators had peer reviewed the national reports published in November last year. It said that some aspects of the stress test definition had been interpreted differently, but that "all countries have taken significant steps to improve the safety of their plants, with varying degrees of practical implementation."

The stress test operation involved all EU nuclear countries as well as Switzerland and Ukraine. Observers included Canada, Croatia, Japan, the UAE and the USA. (Image: ENSREG)

The first among its major recommendations was that the Western European Nuclear Regulators Association (WENRA) should tap further expertise in Europe and "develop guidance on natural hazards assessments, including earthquake, flooding and extreme weather conditions, as well as corresponding guidance on the assessment of margins beyond the design basis and cliff-edge effects."

The next recommendation was that countries urgently implement previously agreed measures to ensure containment at nuclear power plants in accident conditions. For light-water cooled reactors these include equipment, procedures and guidelines to depressurize the primary circuit and prevent core melt at high pressure, prevent hydrogen explosions and prevent overpressure of containment. All these are directly related to the severe conditions seen during the accident sequence at Fukushima Daiichi that resulted in significant loss of containment integrity.

The third recommendation encouraged operators and regulators to get in place various supportive measures that could help prevent accidents or at least limit their consequences. These include bunkered and mobile equipment for instrumentation and communication, emergency response centres and rescue teams.

ENSREG highlighted "the necessity to re-evaluate natural hazards and relevant plant provisions as often as appropriate but at least every ten years."

Energy Commissioner Günther Oettinger said, "This extensive report is a major element of our stress tests. Now, we will do additional visits of power plants and analyse some safety aspects in more detail. EU citizens have the right to know and understand how safe the nuclear power plants are they live close to. Soundness is more important than timing."

ENSREG coordinated the review process, which involved over 70 reviewers from 24 countries as well as EC staff and observers from other countries and the International Atomic Energy Agency (IAEA). As a group they asked over 2000 technical questions of one another and visited 34 power plant sites. ENSREG's summary and its joint statement with the EC was approved by its members (apart from Austria, which abstained) at a meeting on 25 April. The meeting also saw WENRA present proposals on follow-up actions and it was decided that a task force would prepare a program of action including additional site visits and the concept of EU harmonisation of off-site emergency preparedness.

Jointly, the EC and ENSREG are producing an action plan to implement the main recommendations of today's report, participate fully in the IAEA's post-Fukushima action plan, take into account the outcomes from the extraordinary meeting of the Convention on Nuclear Safety, and arrange additional site visits.

Oettinger's department will present the ENSREG report as well as a paper with proposals on nuclear safety to the European Council of heads of state in June.